Infrared ("IR") sensing arrays are widely used to capture images of objects that radiate in the infrared spectrum in applications such as industrial inspection, surveillance, and infrared astronomy. Each element of such sensing arrays has an infrared detector that reacts either to individual incident photons or to the total thermal energy caused by absorption of the incident photons to produce an electrical signal. The electrical signals produced by the sensing array are read out and processed to produce a digital electronic image indicative of an input IR scene.
An IR focal-plane array ("FPA") is an IR sensing array located in a focal plane of an optical imaging module that collects the radiation from a target object so that the image of the target object is focused onto the IR sensing array. Two different configurations, monolithic and hybrid configurations, are usually used to form a photosensing IR FPA. A monolithic FPA has both IR-sensing material and electrical signal transmission paths on the same semiconductor layer. A hybrid FPA separates the IR-sensing material and electrical signal transmission paths into two layers which are aligned with each other and are interconnected with conducting elements (e.g., indium bumps).
However implemented, the image captured by the FPA needs to be read out to a subsequent signal processing circuit. The amount of information contained in the image increases with the number of pixels in the EPA. The speed of transferring this data usually forms the bottle neck of the data processing and significantly affects the frame rate of the imaging system.
High-speed IR images are desired in many applications that sense a moving object or certain transient phenomena such as a rapid change in the object temperature. Conventional IR imaging systems use different approaches to increase the frame rates.
For example, one technique implements one or more moving mirrors to achieve high frame rates. An IR imaging device manufactured by Ellis Camera Company is such an example. A polygon mirror with 6 facets may spin at a rate of 20,000 rotations per second. This produces a frame rate of 120,000 frames per second. A higher frame rate using this technique is usually difficult to achieve due to the inherent limitations of material strength and mirror balance.
Another technique implements a partially parallel data acquisition scheme in a FPA system to achieve a frame rate up to about 32,000 frames per second. Amber infrared camera developed for Wayne State University, connects four digitizers in parallel with respect to one another to simultaneously read out and digitize signals from four adjacent pixels in the FPA. An image is captured by scanning out data from the FPA with four pixels at a time.
The present invention provides an infrared imaging system and method based on a FPA to achieve imaging frame rates up to and greater than about 1 million frames per second.